I love dabbling in photography, pictures of my daughter and friends kids, dogs/animals. We are currently renovating the house (no walls downstairs right now) and OH wants me to have a "space" so I'm not always having my things in the living room. We have the option to start from scratch right down to where electrical outlets and stuff will go.

Our ceilings downstairs are at least 9' so that may work, fingers crossed. Right now I'm looking at (I think) a space that is around 11'x14', so maybe doable... and we have an adjacent family room (2nd) that is 15'x18' so maybe will be able to work something out

It really deppends on who and how many your taking a picture of. And if you sit them or not.

Obviously you will need some sort of back drop. You will want a couple feet between it and your subject. And if you use any kind of lighting on the back drop or back lighting on the subject you will need some room for that. So maybe leave 2-3' from where the backdrop will be if not a little bit more. Have the person stand there. Then back up to where you can place the camera. Remember longer lenses have a slimming effect and wide lens has a wide distortion effect on part of the subject closer to the lens. Alot of people like using 85-105mm for portraits (35mm equavillant), some even longer lenses. So the depth of the room deppends on the focal length you want to use and how much of the scene you want to capture (feet to head, upper body, head shots).

Ceiling height deepends on if your standing your participants, sitting them, or something in between, and if you want to use hair lights or some other upper lighting option on a boom (or ceiling mounted). And obviously standing a tall person in an 8' ceiling room and trying to use a hair light will be hard to do.

So, I am guessing you have a crop sensor camera so a 50-70mm would be a good range for portraits. Grab your camera and do some checking in the rooms your considering. See what you have to work with. Obviously the larger the room the better. Also remember going from corner to corner in the room may give you more distance deppending on how wide you want your backdrop to be.